\[4b^{2} - 16b + 12 = 0\ \ \ \ |\ :4\]
\[b^{2} - 4b + 3 = 0\]
\[D = 4 - 3 = 1\]
\[b_{1} = 2 + 1 = 3;\ \ b_{2} = 2 - 1 = 1.\]